Short-arc lamp having an improved prefocus base,and method of prefocusing said base



July 8, 1969 R. F. VAN CLEAF 3,454,810

SHORT-ARC LAMP HAVING AN IMPROVED PREFOCUS BASE, AND METHOD OI PRIi-FOCUSING SAID BASE Filed Dec. 19, 1966 x /IHUL, c 1 I 1 true 28. I I 30 k -22 32 .I I W A se 1w I 20. I I I 24 is J; 28 I '5 INVENTOR WITNESSES I fill/ 1 I Rancid F, Van Clegf t y egg;

3,454,810 SHORT-ARC LAMP HAVING AN IMPROVED PRE- FOCUS BASE, AND METHOD OF PREFOCUSING SAID BASE Ronald F. Van Cleaf, Bloomfield, N.J., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 19, 1966, Ser. No. 602,629

Int. Cl. H01j 61/06 US. Cl. 313-214 Claims ABSTRACT OF THE DISCLOSURE Background of the invention This invention relates to electric lamps and has particular reference to an improved prefocus type base for short-arc gaseous discharge lamps and to a method for accurately aligning such bases with the lamp electrodes. In certain lighting applications short-arc lamps are used with optical or reflector systems. In such applications it is accordingly necessary that the electrodes be accurately aligned with the base structures at each end of the lamp so that the arc will be properly oriented with respect to the optical or reflector system when the lamp is placed into its fixture and operated. The positioning of the are or light source is so critical in some cases that axial alignment of the electrodes and the socket-engaging portions of the base within a tolerance of 0.005" is specified.

Heretofore, the axial misalignment of the bases and their respective electrodes which unavoidably occurs due to ececntricities introduced during the sealing of the envelope arms was corrected by adjusting and checking the orientation of the base members relative to the electrode tips before the bases were rigidly clamped to the sealing arms. However, this procedure was tedious, inefficient and did not provide the precision required to meet the desired tolerances. Others have attempted to solve this problem by properly positioning a disc-shaped element in abutting relation with the end of the base cap and then spot welding the members together. This technique is disclosed in French Patent No. 1,392,174, dated Mar. 12, 1965. However, it is not entirely satisfactory since it requires a crtical welding operation and presents a problem where tolerances in the order of thousandths of an inch are involved insofar as the heating and differential expansion and contraction of the lamp parts resulting from the spot welding operation is sufficient to upset the alignment. The same difliculties arise when a two-piece base assembly is used and one part is aligned with the electrodes and then brazed to the previously attached part of the assembly.

Summary of the invention It is accordingly the general object of the present invention to provide an improved electric lamp containing a concentrated source of light that is precisely oriented with respect to the base structure. In particular, the invention is directed to a short-arc discharge lamp having a cathode and a prefocus base that are axially alinged with snfiicient accuracy to meet a specified tolerance limit.

ted tates atent Another object is the provision of an improved prefocus base for short-arc lamps and the like that is cheap, easy to assemble and provides means for establishing a precise prefocus alignment between the base members and lamp electrodes.

A further object is a method for quickly and accurately checking and correcting the axial misalignment of the base members and electrodes of a short-arc lamp.

In the case of a short-arc lamp, the aforesaid objects and other advantages are achieved in accordance with the present invention by positioning an eccentrically-rotatable depending focusing pin on the end of each of the base caps or sleeves attached to the sealing arms of the envelope. Proper orientation of the focusing pins is accomplished according to the preferred method by holding the lamp stationary on a predetermined axis and rotating the pins until the tips of the electrodes are aligned with the aforesaid axis. The pins are then mechanically locked in place on their respective base sleeves by means of lock washers and screws.

Brief description of the drawing FIG. 2 is an enlarged exploded view of one of the prefocus base assemblies shown in FIG. 1;

FIG. 3 is a side elevational view of one form of apparatus for axially aligning the lamp electrodes with their respective base pins; and

FIGS. 4 and 5 are views of the lamp electrodes as seen through the upper and lower microscopes, respectively, of the focusing apparatus shown in FIGS. 1 and 3.

While the present invention can be used with advantage in the manufacture and basing of various types of lamps that contain concentrated sources of light, it is particularly adapted for use in conjunction with short-arc discharge lamps and has accordingly been so illustrated and will be so described.

Lamp and prefocus base structure customary oppositely-disposed cylindrical sealing arms 13 and 14. An enlarged tungsten anode 15 is anchored in the arm 13 and electrically connected by a series of sealed-in ribbon conductors 17 to a flexible power lead 19. A pointed rod cathode 16 of tungsten is anchored in the other sealing arm 14 and connected by another set of ribbon conductors 18 to a second power lead 20. The sealing arms 13 and 14 are provided with prefocus base assemblies B and B, respectively, that are rigidly fastened in enclosing relationship with the ends of the arms by metal clamping rings C, C. The base assemblies are terminated by focusing pins 23, 24 of cylindrical configuration that are mechanically locked in place and adapted to seat in the fixture or socket in which the lamp will be used.

The pins 23, 24 thus control the orientation of the electrodes 15, 16 relative to the fixture and associated reflector system etc. The lamp 10 is energized by the separate power leads 19, 20 which are connected to suitable terminals in the mixture.

Each of the aforementioned base assemblies are identical and the one depicted in the lower portion of FIG. 1 is illustrated in detail in FIG. 2 and will now be described. As shown, the base assembly B consists of a hollow cylindrical body portion or sleeve 22 of suitable 3 metal, such as stainless steel, one end of which is provided with a series of spaced slots 25 and flexible tongues 27 that render it expandible. The other end of the sleeve 22 is closed by a perpendicular end wall 28. A suitable axially extending appendage such as a hollow stud 30 of circular cross-section protrudes from the end wall 28 and receives the focusing pin 24 which, as shown, is cylindrical and has an aperture 26 that is off-set from the axis of the pin and is slightly larger in diameter than the stud 30. The focusing pin 24 is thus freely rotatable about the stud 30 and can be securely locked in abutting relation with the end wall 28 and sleeve 22 by a lock washer 36 and metal socket-head cap screw 38 which engages threads 32 formed interiorly of the stud.

A slot opening 34 near the closed end of the sleeve 22 permits the power leads to be brought on: through the sides of the bases.

The base assemblies B and B are rigidly attached to the respective sealing arms 13 and 14 in the conventional manner by first wrapping the arms with wet asbestos tape, slipping the sleeves 21, 22 over the arms and wrappings, and then constricting the' slotted ends of the' sleeves by tightening the clamps C and C and allowing the asbestos tape to dry.

Pre focusing apparatus A preferred aparatus for checking and correcting the axial misalignment between the anode 15 and the cathode 16 and their respective base assemblies B and B is ilustrated in FIG. 3. As shown, the apparatus comprises a jig 40 having a base plate 42 and a pair of upstanding support blocks 44, 45 that are spaced 'apart (see FIG. 1) a distance equivalent to the distance between the ends of the base sleeves 21 and 22 so that the cylindrical focusing pins 23, 24 rest in V-shaped notches 46, 47 provided in the blocks. The lamp 10 is placed in the jig 40 with the focusing pins cradled in the notches, as shown in FIGS. 1 and 3. The lamp is thus supported solely by the focusing pins.

The lamp 10 is desirably enclosed by a protective plastic jacket 48 (shown in dotted outline in FIG. 3) during the pefjpcusing operation as a safety measure. The pins 23, 24 can be locked in cradled position in the jig 40 by hinged latches 49 carried by each of the support blocks 44, 45. These latches, when lowered into position over the focusing pins, are retained in such position by tightening screws 50 that engage threaded holes in the blocks. The pins are prevented from rotating by set screws 51 carried by each of the latches 49.

A centrally located support arm 52 which extends upwardly from one side of the base plate 42 holds a pair of microscopes 53 and 54 directly above and to the side, respectively, of the lamp 10. That is, the microscopes are spaced 90 degrees apart with respect to the lamp axis. The longitudinally-extending cross-hairs of the microscopes are aligned with an axis that bisects the notches 46, 47 and are coincident with the axes of the cylindrical pins 23, 24 when the latter are seated in the support blocks 44, 45. This alignment is achieved with a suitably designed gauge. The tips of the electrodes are thus in the field of view of both microscopes, as shown in FIGS. 4 and 5.

Prefocusing method The lamp 10 with its protective plastic jacket 48 is placed in the jig 40 with the loosely attached focusing pins 23, 24 resting in the notched support blocks 44, 45 as shown in FIGS. 1 and 3. The lamp 10 is then held stationary and the pin 24 is slowly rotated as it rests in the notch 46 and the lamp is supported solely by the pins. The resultant movement of the cathode 16 relative to the axial cross-hairs 55, 56 (see FIGS. 4 and is observed through the microscopes 53, 54 while the pin 24 is being rotated.

Since the axis of the focusing pin 24 is off-set with respect to its aperture 26, the tips of the anode 15 and cathode 16 will shift from side to side as they are viewed through the microscopes and the pin is being rotated. This shifting is indicated by the dotted outlines of the electrode tips as shown in the field of view of microscope 53 illustrated in FIG. 4.

The pin 24 is simply rotated until the cathode tip is aligned with the axial cross-hairs 55, 56 of the microscopes 53, 54. The latch 49 is then lowered and locked in such position by screw 50, and set screw 51 is tightened against pin 24 to prevent it from rotating. Pin 24 is then locked in place by tightening the cap screw 38. The same operation is performed at the opposite end of the lamp 10 to align the anode 15. Since the focusing pins 23, 24 are seated in the V-notches 46, 47 and the axial cross-hairs 55, 56 have previously been aligned with the fixed axis that bisects the notches and is coincident with true axes of the pins, the electrodes are automatically axially aligned with their respective pins and the aforesaid fixed axis.

The latches 49 are then released and the lamp 10 is rotated through 360 together with the locked focusing pins 23, 24 while the tips of the anode 15 and cathode 16 are again observed through the microscopes 53, 54. The tips of the electrodes should remain centered on the respective cross-hairs 55, 56 since the pins and electrodes are axially aligned. If the tips of the anode 15 or cathode 16 shift any appreciable degree from the reference lines 55, 56 as the lamp 10 is rotated through 360', then the locking screws 38, 39 and pins 23, 24 are loosened and the latter are rotated slightly until a balance is obtained between the deviations from the reference lines 55, 56 observed through the respective microscopes. The locking screws are then retightened, thereby completing the operation.

Experience has shown that a skilled operator can axially align the base pins and electrodes of a short-arc lamp within several thousandths of an inch in a few minutes using this technique and apparatus.

The efficiency and accuracy of the prefocusing operation can be further improved by providing a series of focusing pins of the same overall dimensions but having apertures that range from zero eccentricity to 0.050" eccentricity, in steps of 0.010". Focusing pins having zero eccentricity are first slipped over and locked on the base studs and the lamp is placed in the jig and rotated. The electrodes are then observed through upper microscope 53 and the degree of eccentricity is read directly from the graduated scale S (see FIG. 4). If this preliminary check shows, for example, that the electrodes are 0.025 out of alignment, then the lamp is removed from the jig,

focusing pins having 0.025" eccentricity are placed on the studs, and the focusing procedure is carried out.

This arrangement permits the alignment of each electrode to be separately controlled and maintained within very close tolerance limits insofar as a focusing pin having an eccentricity that matches that of the respective pairs of electrodes and studs can be used.

If desired, the focusing jig can also be used to control the light center length dimension of the lamp 10; that is, the distance between the tip of the cathode 16 and the end wall 28 of the base sleeve 22 attached to arm 14 of the envelope 12. This can be achieved by positioning the lower microscope 54 so that its vertical crosshair 57 (FIG. 5) is spaced a corresponding distance X (see FIG. 1) from the inner face of support block 44. The lamp 10 is placed in the focusing jig 40 immediately after the base assemblies are slipped over the sealing arms and wet asbestos wrappings. When the base sleeve 22 is adjusted so that the cathode tip just touches the cross-hair 57 as shown in FIG. 5, the asbestos wrappings are force-dried (as by a stream of hot air) and the sleeves are rigidly fastened to the respectiye arms by tightening the clamps C and C.

It will be appreciated from ,the foregoing that the objects of the invention have been achieved in that an improved short-arc lamp having precisely oriented and inexpensive pre-focus type base assemblies has been provided. A simple efiicient method for precisely orienting the fixture-engaging portions of the bases and one form of apparatus for practicing the method have also been provided.

While a preferred lamp-and-base embodiment and prefocusing method have been disclosed, it will be appreciated that various modifications can be made without departing from the spirit and scope of the invention. For example, it is entirely within the scope of the invention to determine the proper orientation of the eccentric focusing pins by holding the pins stationary relative to the jig and rotating the lamp. While this is a more awkward and time-consuming procedure, the pins and respective electrodes can be aligned with approximately the same degree of accuracy as when the preferred method is used.

I claim:

1. In an electric lamp having an envelope that contains a concentrated source of light and has an elongated end portion that is sealed and is slightly eccentric with respect to a predetermined axis that passes through said end portion and said light source, the improvement comprising an integral prefocus base assembly having a body portion that is rigidly attached to the sealed end portion of said envelope and is also out of alignment with said predetermined axis, and' a depending adjustable focusing member that is mechanically fastened to said body portion in predetermined eccentric relationship therewith so that the axis of said member is substantially aligned with said predetermined axis and said concentrated light source,

said focusing member constituting the fixture-engaging portion of said base assembly that controls the position of said light source when the lamp is placed in its fixture and is in use.

2. The invention set forth in claim 1 wherein;

said lamp comprises a high-intensity electric discharge lamp having a pair of spaced oppositely-disposed electrodes,

the elongated sealed end portion of said envelope comprises a generally cylindrical vitreous arm in which one of the electrodes is anchored,

said predetermined axis passes through said one electrode,

and the body portion of -said base assembly comprises a cylindrical sleeve that encircles and encloses the end of said vitreous arm.

3. The invention set forth in claim 2 wherein;

said electric discharge lamp comprises a short-arc lamp having an envelope with a pair of opposed vitreous arms each of which is provided with a prefocus base assembly,

said electrodes comprise an anode and a cathode that are anchored in the respective vitreous arms, and

said focusing members are attached to the ends of the respective base sleeves and are so oriented that their respective axes are substantially aligned with the predetermined axis that passes through the associated arm and electrode.

4. An adjustable prefocus base assembly for a highintensity electric discharge lamp or the like comprising;

a hollow metal sleeve having a wall at one end from which an interiorly-threaded stud of cylindrical configuration extends,

a metal focusing pin rotatably disposed on said stud and having the configuration of a cylinder that is eccentric with respect to said stud and sleeve, and

fastening means engaging the threads of said stud and adapted, when tightened, to mechanically lock said focusing pin on the end of said metal sleeve in predetermined eccentric relationship therewith.

5. The prefocus base assembly set forth in claim 4 wherein;

said metal sleeve is of cylindrical configuration,

one end of said sleeve is closed by said wall and the opposite end of said sleeve has a plurality of longitudinal slots therein that render it expandible, and said fastening means comprises a screw and a lock washer. 6. In the manufacture of an electric discharge lamp having an envelope containing an electrode that is visible through said envelope and is anchored in a depending sealed portion of said envelope that is terminated by a base member which is attached to said sealed portion and thus constitutes an integral part of the lamp, the method of establishing a prefocused relationship between said base member and electrode and thereby correcting to a preselected tolerance the axial misalignment thereof that inherently occurs when said electrode is anchored in the sealed portion of said envelope and said base member is fastened to the latter, which method comprises;

providing a fixed axially-extending appendage on the end of said base member,

placing an apertured rotatable cylindrical focusing member on-said appendage, the aperture in said member being otf-set a predetermined distance from its axis so that said member revolves eccentrically about said appendage,

manipulating said lamp and focusing member to produce relative rotational movement therebetween until said electrode is oriented in such a position relative to said focusing member that the axial misalignment therebetween is, reduced to the preselected tolerance,

and then mechanically locking said focusing member in the aforesaid position on said appendage.

7. The method set forth in claim 6 wherein the rotational movement between said lamp and focusing member is achieved by holding the lamp stationary and rotating the focusing member.

8. The method set forth in claim 6 wherein;

said lamp comprises a short-arc lamp containing a pair of elongated electrodes that are anchored in oppositely-disposed vitreous sealing arms that comprise the ends of said envelope,

each of said sealing arms are terminated by a base member that is fitted with an eccentrically rotatable focusing member,

the rotational movement between said lamp and respective focusing members is achieved by supporting the lamp by said members and holding the lamp stationary while the focusing members are rotated, aid

the desired orientation of said focusing members relative to the respective electrodes is determined by observing the electrodes through said envelope and noting the displacement thereof from a fixed axial reference line while the focusing members are being rotated.

9. The method set forth in claim 8 wherein;

the axially-extending appendages are aligned with the axis of the respective base members,

a series of cylindrical focusing members of graduated eccentricities are provided,

a focusing member of zero eccentricity is initially attached to each of said coaxial appendages and the degree of eccentricity of each electrode is noted while the focusing members are rotated relative to said lamp,

the zero-eccentric focusing members are removed and replaced by focusing members having eccentricities that substantially match the noted eccentricities, and

the lamp is again held stationary and the focusing members rotated until the focusing members and respective electrodes are so oriented that the noted eccentricities are corrected to the desired tolerance.

10. The method set forth in claim 8 wherein;

the fixed axial-reference line is established by support-- ing the lamp on a predetermined axis that coincides with the axes of both of said cylindrical focusing members, and

the orientation of said electrodes relative to said reference line is determined and individually by observing the tips of the respective electrodes through a pair of microscopes located laterally of said lamp and spaced approximately 90 degrees apart.

corrected 8 References Cited UNITED STATES PATENTS 12/1921 Minick 24044.Z 3/1951 Isaacs et al. 3l3-2l4 JANIES W. LAWRENCE, Primary Examiner.

R. F. HOSSFELD, Assistant Examiner.

US. Cl. X.R. 

